What they were doing is no different than what thousands of other websites do to game Google. Except that instead of paying for links with money they were paying for them with traffic from tweets.

I don't really understand why buying links is suddenly called "growth hacking" when a startup does it.

Seems like anything that is "hustling" is called "growth hacking" now a days. We applaud startups that make it to the big leagues and idolize how much they hustle and break the rules and then when someone does break the rules, everyone jumps in to tell them how bad they are.

What the investors want or do is their responsibility; what funded companies do is their own and expectations of VCs are no excuse for such practices. They're not "necessary" by any means unless the company has a business model centered on spamming.

This unfairly ignores the influence investors can have on the company. Investors have a timeline for getting a return on money, known as investment horizon. Sometimes their bets don't work out, and sometimes the horizon is a bit too aggressive for the company. But when the investors normally have board seats and possibly other vectors of influence, you can't ignore how an investor's investment horizon influences strategic business decisions.